Here’s my take on this.
I can see both sides of the argument for using technology in these situations. On one hand, a dedicated monitoring application can provide direct answers. These tools are designed to give you a clear picture of communications, social media usage, and location history from the S21, which can either confirm your fears or provide peace of mind.
On the other hand, there are less invasive built-in features to consider. For instance, Android’s own Find My Device or Google’s Location History (if enabled) can show a phone’s recent locations. Looking at synced account activity can also provide clues. It’s a difficult position, as the information you find—or don’t find—will lead to its own set of challenges and next steps.